In order to improve reliability, such a system is used in which a plurality of servers are combined to provide a redundant configuration (for instance, reference may be done to Patent Literature 1). For example, a duplex system comprises two servers having the same configuration, and, when one active (active) server (also termed as “operation system” server or “working system” server) fails, the system switches to and operates with a normal server apparatus (also termed as standby server (also termed as “waiting system” server or “reserve system” server)).
(N+1) redundancy system is a system wherein one server apparatus is arranged as a common reserve apparatus (standby server) for N number of server apparatuses (active servers).
In a hot standby system, for instance, data is synchronized between an active server and a standby server such that the standby server can take over service (processing) in an instant, when the active system server fails.
In a so-called cold standby system, a standby server stands by in a stopped state, and when an active server fails, the standby server is started up to switch over the operation and processing. The cold standby system, in which starting up and preparation of the standby server are executed after the active system server fails, has limitation in terms of system downtime and service continuation.
In a system called a warm standby (Warm Standby) system, when an active server operates, a standby server stands with power set on and with OS (Operating System) booted up (with database content being copied asynchronously), and, when the active system server fails, with network switching or the like, a user program such as a business application is invoked, and processing is transferred to the standby server.
Patent Literature 2 discloses the following server system. Out of servers each operating as an active system, a server in which a software for update is stored, transmits the software for update other server and instructs all servers each operating as a standby system to update to the software for update. When the update instruction is issued, the servers each operating as a standby system update software running on these servers to the software for update. After all the servers each operating as a standby system complete the update, the server in which the software for update is stored, switches active systems and standby systems of all of the set of servers.
Patent Literature 3 discloses the following system. The system comprises first and second databases operating on virtual machine with different performances, and exchanges virtual machines used by the system in response to an external instruction to perform scale up or scale down the performance of the system. At this time, the system performs data synchronization of the databases using a stream type replication function provided in each of the databases. After establishment of the data synchronization, the virtual machine that forwards an SQL (Structured Query Language) command is switched to another virtual machine. This configuration dynamically and inexpensively achieves the scale-up/down of a database equipped with a stream type replication function by utilizing the stream type replication function without stopping a Web service.
As a technology of virtualizing network functions, in addition to virtualization computing and storage of a server, NFV (Network Functions Virtualization) and so forth that realizes network functions by means of software using an application or the like running on a virtual machine (VM) implemented on a virtualization layer such as a hypervisor on a server is known. NFV is realized by a virtualization technology on a general-purpose server, as opposed to dedicated appliance (e.g., LTE (Long Term Evolution) mobile network node (e.g., MME (Mobility Management Entity), P-GW (Packet data network Gateway), S-GW (Serving Gateway), etc.)), and the functions can be changed by means of software at any time (e.g., refer to Non-Patent Literature 1).
[Patent Literature 1]
    Japanese Patent No. 4479930B[Patent Literature 2]    Japanese Patent No. 5011655B[Patent Literature 3]    Japanese Patent Kokai Publication No. JP-P2012-215937A[Non-Patent Literature 1]    ETSI GS NFV 002 V1.2.1 (2014-12), Network Functions Virtualisation (NFV); Architectural Framework, pp. 13-18, searched on Dec. 25, 2014, the Internet <URL: http://www.etsi.org/deliver/etsi_gs/NFV/001_099/002/01.02.01_60/gs_NFV002v010201p.pdf>